Enclosed hopper cars with pneumatic systems for unloading the car are well known and frequently used for the transportation of powdered and granular products. For cars with positive pressure pneumatic systems, air is generally supplied from an external source to pressurize the car and simultaneously fluidize the dry, bulk product carried within the car to permit easy discharge from the car. Air pressure within the hopper car during the unloading procedure is typically maintained at 15 PSI.
Frequently, the pneumatic discharge or unloading system associated with pressurized hopper cars will include an air control valve to divert a portion of the air supplied to the hopper car directly into the discharge line. The air pressure in the discharge line is generally maintained at 2 or 3 PSI below the pressure within the hopper car. Pressurized hopper cars with this type of pneumatic unloading system are often referred to as pressure differential cars or pressure discharge cars. Trinity Industries, Inc. manufactures and sells Power Flo.RTM. cars with the previously described pneumatic unloading system.
An example of aeration equipment and a pneumatic discharge system for removing dry, bulk material from hopper style containers is shown in U.S. Pat. No. 3,929,261 entitled "Aeration Device and Method for Assisting Discharge of Material from Containers." This patent is incorporated by reference for all purposes within this application.
Flour, starch and similar food products are examples of dry, bulk material suited for loading, transportation and discharge with an enclosed hopper car having a positive pressure pneumatic unloading system. Any dry powder, granular, or pellet shaped commodity may be satisfactorily transported in such hopper cars. An enclosed hopper car in cooperation with the pneumatic system protects the contents of the car and minimizes loss during the loading, transportation, and the discharge process. Also, pneumatic handling is often the most cost effective, efficient method to handle large quantities of dry, bulk products.
For optimum loading and unloading, interior portions of the railway car are frequently divided into multiple funnel shaped sections or hoppers. Hence, these cars are frequently referred to as "hopper cars." In an effort to maximize the carrying capacity of hopper cars while maintaining a relatively low center of gravity and a relatively low profile to minimize wind resistance, the bottom of each hopper section in the associated hopper car is placed relatively close to the railway track clearance line (vertical curve).
Connections with the hopper car's pneumatic discharge line are generally placed at or near the lowest portion of each hopper section to ensure removal of all product within the car. Due to the requirement for clearance of the railroad track and limitations as to the overall size of pressurized hopper cars, previous cars have generally been limited to a discharge line having an outside diameter of six inches or less. A five inch discharge line is typical for many pressure differential cars.
The types of dry, flowable material carried in pressurized hopper cars has increased significantly and includes a wide range of new products such as fly ash produced from burning large quantities of coal at electrical generating facilities. Considering the generating capacity of a modern electrical plant, it has become increasingly important to be able to rapidly discharge the contents of a pressurized hopper car containing fly ash. Thus, a need has arisen for an improved pressure differential hopper car which has larger diameter discharge piping without requiring substantial modification to existing pressurized hopper car bodies.